WASHINGTON (USA TODAY) - Attorney General Eric Holder acknowledged Wednesday that four U.S. citizens had been killed in counter-terrorism drone strikes since 2009.

In a letter to Senate Judiciary Committee Chairman Patrick Leahy, Holder said only one of the four, radical cleric Anwar al-Awlaki, the inspiration for several plots against the U.S., was "specifically targeted'' in counter-terrorism operations against al-Qaeda.

Three others, including al-Qaeda propagandist Samir Khan, Al-Awlaki's son, Abd al-Rahman, and Jude Kenan Mohammed were killed during the same time period but "these individuals were not specifically targeted by the United States.''

Holder said the letter, directed by President Obama, comes in response to congressional inquiries about the "administration use of lethal force against U.S. citizens.''

The five-page communication comes in advance of Thursday's scheduled national security speech by President Obama and attempts to address one of the most volatile issues in the nation's counter-terrorism strategy.

"Based on generations-old legal principles and Supreme Court decisions handed down during World War II, as well as during the current conflict, it is clear and logical that United States citizenship alone does not make such individuals immune from being targeted,'' Holder wrote in the letter, which also was transmitted to other congressional leaders.

"Rather, it means that the government must take special care and take into account all relevant constitutional considerations, the laws of war and other law with respect to U.S. citizens - even those who are leading efforts to kill their fellow, innocent Americans.''